Application of conductive coating to cathode ray tubes



June 10, 1958 A. P. JOHAN'SEN 2,837,754

* APPLICATION OF commcnvs poA'rI'NG T0 CATHODE RAY TUBES Filed May 17, 1956 ATTORNEYS APPLICATION OF CONDUCTIVE COATING TO CATHODE RAY TUBES Application May 17, 1956, Serial No. 585,538

6 Claims. or. -22

This invention relates to an apparatus for applying coatings to the interior surfaceof vessels and more particularly relates to an apparatus for applying coatings to the internal surfaces of glass envelopes for cathode ray tubes.

These glass envelopes, known in the art as cathode ray tube blanks, include a substantially closed and generally conically shaped vessel portion the interior of which is accessible only through a restricted aperture called the neck. When cathode ray tubes are utilized in television and similar applications it has been found that a portion of the enclosing envelope in the vicinity of the electron beam becomes electrically charged to affect the electron beam in a deleterious manner. In order to prevent this it is customary to coat the internal surface of this portion of the envelope with a conductive material which may have a suitable potential applied thereto to provide a field for focusing the electron beam which is projected towards a screen at the large end of the enclosing envelope. The conductive coating generally used in this application is colloidal graphite suspended in an aqueous vehicle.

The most common current method of applying this coating involves rotating the cathode ray tube blank upon a suitable work stand while inserting non-revolving brushes through the neck aperture. The non-rotating brush is supplied with coating material, through a prior dipping or otherwise, and applies a coating to the internal walls of the cathode ray tube blank. While this method is effective in providing the desired coating on the internal surface of the cathode ray tube blank it is possessed of a number of inherent disadvantages which are considered to be quite serious. Thus the rotation of the cathode ray tube blank requires specially constructed equipment which is generally relatively expensive and, since the blank must be mounted on and removed from this additional piece of equipment, the cost of production is increased Without in any Way increasing the value of the tube. Where this method is carried out automatically, as is usually the case, the cost of the automatic mechanical equipment is relatively high.

By means of the apparatus of this invention it has now been found that the foregoing coating step may be carried out while the cathode ray tube blank is on a conventional material handling conveyor of the type generally used in its transportation without the necessity of additional equipment. Handling of the blank onto and from an additional mechanical device is eliminated, as

is the special equipment itself, thereby materially reducing both equipment and manpower costs in producing the tubes. While the apparatus of the invention may be quite satisfactorily operated by hand, it is also possible to provide for its use in a simplified automatic machine.

It is accordingly a primary object of the present invention to provide an improved apparatus for applying coatings to the interior surfaces of vessels.

It is another object of the invention to provide an improved apparatus for applying coatings to the interior surfaces of cathode ray tube blanks.

These and further objects and advantages of the invention will become apparent upon reference to the following specification, claims and appended drawings wherein:

Figure l is a vertical elevation of a cathode ray tube blank;

Figure 2 is a vertical elevation of an apparatus for coating one portion of the interior surface of the blank of Figure 1 according to the invention; and

Figure 3 is a vertical elevation of another device for coating the interior surface of the cathode ray tube blank of Figure 1 according to the invention.

Referring to Figure 2 there is shown a coating apparatus consisting of a handle 10 having a hollow slide tube 12 attached thereto. The slide tube 12 is of a length approximately equal to the length of the neck 25 of the tube blank to be coated. Rotatably and removably mounted in the handle it] and tube 12 is a spring wire 14 which has its end connected to a crank 16 for imparting rotation thereto. The spring wire 14 has a permanent set which causes that portion of it which extends beyond the tube 12 to curve, as is shown at 18. A brush it) is mounted upon the curved end of the spring wire 14 by means of a clip 22.

The brush shown in Figure 2 is utilized to coat the area A of the cathode ray tube blank 23 in Figure 1 as follows: The spring wire 14 is retracted within the tube 12 and handle 10 by withdrawing the crank 16 to the right in Figure 2 until the brush abuts the end of the tube 12. A conductive coating is then applied to the brush by any suitable means and the brush is then inserted 'into the neck 24 of the cathode ray tube blank until the handle 10 engages the flared mouth 25 of the neck 24. During this operation the brush is maintained out of contact with the interior of the neck. The crank 16 is then pushed upwardly until the brush 20 and spring wire 314 are fully extended, in which position thespring wire assumes the position dictated by its permanent set and forces the brush 20 against the interior wall of the bulb at the approximate positionof 26 in Figure 1. The crank 16 is thereupon rotated and simultaneously pulled down to coat the area shown at A in Figure 1. When this area has been coated the brush is fully retracted and the apparatus of Figure 2 is withdrawn from the neck of the cathode ray tube blank.

Through the use of this simple apparatus and process it is possible to coat the irregularly shaped interiors of the cathode ray tube blanks which previously have been coated only by means of highly complex and costly machinery. q

Referring to Figure 3 there is shown a coating apparatus 28 which is utilized to coat the area B in the neck 24 of the cathode ray tube blank 23. This device consists of a handle 30 having an enlarged end portion 32 with a beveled edge 34. A slide tube 36 is mounted through thehandle 3t} and receives a solid shaft 38 which may be rotated and axially moved by means of a crank 40. A brush 42 is mounted upon the other end of shaft 38 by means of a clip 44. A guide 46 having an offset 58 is attached to the enlarged section 32 of handle 30 by means of a leg 43 and has mounted at its other end a semicircular bracket 5t having a diameter substantially equal to that of the neck 24 of the cathode ray tube blank 23.

The area B of the cathode ray tube blank shown in Figure 1 is coated by means of the apparatus of Figure 2 as follows: The shaft 38 is retracted into the slide tube 36 and handle 30 by pulling the crank 40 to the right in Figure 3 and a coating material is applied to brush 42. The brush is then inserted into the neck of the Patented June 10, 1958 cathode ray tube blank until the beveled edge 34- of enlarged section 32 on handle 3% rests against the flared section of neck 24. During this insertion the backside 54 of the brush is maintained in close proximity to the interior Wall of neck 24 so as to avoid coating the interior wall of the neck as the brush is moved into position. This is accomplished by insuring that the semicircular bracket 50 is as far from the neck as possible and this permits the bracket 50 to pass over the flared portion 25. After the beveled portion 34 of handle is seated against the flared portion 25 of the tube neck 24 the back 54 of the brush 42 is still maintained proximate the interior wall of the neck 24 and the crank is moved upwardly to extend the brush to approximately the position 56 in Figure 1., The semicircular bracket is then forced against the outside surface of the neck to place the brush 42 in contact with the interior surface of the tube and the crank as is rotated while being slowly drawn downwardly until area B is coated. The device 28 is then again canted to place the back of brush 54 proximate the interior wall of the neck and the crank 40 drawn downwardly to withdraw the brush. The

- brush is then withdrawn from the neck of the tube in the same manner in which it was inserted. The offset in the guide 46 provides space for the flared portion 25 of neck 24 when the bracket 50 is located against the exterior surface of the neck. It will be understood by those skilled in the art that design variations are possible to take into account unconventionally shaped vessels, and

to combine the action of several brushes in one design to meet a specific series of contours.

It will be apparent from the foregoing that by means of the apparatus disclosed herein it is possible to coat the interior surface of a vessel having an irregular cross section without the use of expensive equipment and without the necessity of ever removing the vessel from the conventional conveyors upon which it is normally handled.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the mean ing and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. An apparatus for coating the interior surface of a vessel having an irregular shape comprising, a handle, a tube extending from said handle, a spring wire movably extending through said tube and handle, said wire having a permanent set and being substantially longer than said tube and handle, said wire being axially movable and rotatable Within said tube, a brush mounted on the end of said wire extending from said tube, and means for rotating said wire mounted on the end thereof extending from said handle.

2. An apparatus for coating the interior surface of a vessel having an irregular shape comprising, a handle, a tube extending from said handle, a spring wire movably tubular vessel comprising, a handle, a tube extending from said handle, a shaft movably extending through said tube and handle and being substantially longer than said tube and handle, said shaft being axially reciprocable and rotatable within said tube, a brush mounted on the and of said shaft extending from said tube, and a crank mounted on the end thereof extending from said handle.

4. An apparatus for coating the interior surface of a tubular vessel comprising, a handle, a tube extending from said handle, a shaft movably extending through said tube and handle and being substantially longer than said tube and handle, a brush mounted on the end of said shaft extending from said tube, a crank mounted on the end thereof extending from said handle, a guide member attached to said handle and extending along said tube, and a bracket attached to the free end of said guide member.

5. An apparatus for coating the interior surface of a tubular vessel comprising, a handle, a tube extending from said handle, a shaft movably extending through said tube and handle and being substantially longer than said tube and handle, a brush mounted on the end of said shaft extending from said tube, a crank mounted on the end thereof extending from said handle, a guide member extending along the side of said tube and having a bent portion thereof attached to said handle, said guide member having an offset therein whereby the portion of said guide member adjacent said handle is spaced from the axis of said handle by a greater distance than is the free end of said guide member, and a semicircular bracket attached to the free end of said guide member.

6. An apparatus for coating the interior surface of a vessel having an irregular shape comprising, a handle, a tube extending from said handle, a spring slide extending through said tube and handle and being substantially longer than said tube and handle, said spring slide being rotatable and axially reciprocable within said tube and having a permanent set which causes said spring slide to curve when any appreciable portion thereof extends beyond the end of said tube, a brush mounted on the end of said spring slide extending from said tube, a crank mounted on the end of said spring slide extending from said handle, a guide member attached to said handle and extending along said tube, and a bracket attached to the free end of said guide member.

References Cited in the file of this patent UNITED STATES PATENTS 1,014,236 Lawhon Jan. 9, 1912 1,203,636 Louis Nov. 7, 1916 1,679,166 Murdock July 31, 1928 1,905,656 Smith Apr. 25, 1933 2,342,833 Borgeat Feb. 29, 1944 

